1. Field of the Invention
The present invention relates to a fixing device which is employed in, e.g., a copying machine or printer apparatus using toner, and fixes a toner image onto a medium to be transferred.
2. Description of the Related Art
A fixing device which is assembled into a copying machine using an electrophotographic process heats and melts toner on a medium to be transferred, and fixes the toner onto the medium.
As a toner heating method usable in the fixing device, a method using radiation heat obtained by turning on a filament lamp, and a flash-fixing method using a flash lamp have widely been known. Recently, a fixing device using an induction heating device as a heat generation source is put into practical use.
In many cases, the fixing device uses a heat (fixing) roller which incorporates a heater, and a press roller which is pressed against the heat roller at one point on the outer surface of the heat roller at a predetermined pressure. With this structure, heat can be efficiently supplied from the heat generation source to toner. A pressure for fixing melted toner onto a medium to be transferred can be easily applied to the medium and toner.
Most of toners used in a copying machine and printer apparatus are granular particles or powder particles prepared by coating a pigment or dye with a hot-melt resin. Toner which is not fixed to a medium to be transferred often remains at a portion of the fixing device which contacts melted toner. Thus, many fixing devices having a cleaning device which recovers toner left on the heat roller are commercially available.
As a method of cleaning the heat roller, felt is brought into contact with the outer surface of the heat roller, and oil which prevents toner from attaching to the heat roller is supplied. Toner is fixed to a portion where it is brought into contact with the heat roller in the use of felt. Thus, the felt is formed into a roller shape to prevent toner from being fixed to one portion.
Even with the felt roller, the toner recoverable amount decreases and the image quality degrades during the maintenance cycle because of an increase in the image forming speed of a copying machine and printer apparatus and prolongation of the maintenance cycle of the copying machine and printer apparatus. If felt containing a large amount of toner is pressed against the heat roller for a long time, the heat roller surface is scratched.
To solve these problems, a web cleaning method of changing (shifting) the position of felt brought into contact with the heat roller in accordance with the cumulative image forming count (lapse of a predetermined time).
In the use of the felt web, the web containing toner is sequentially taken up. The replacement time of the cleaning device can be set by setting the web amount in accordance with the maintenance cycle. The web may be coated with oil which prevents toner from attaching to the heat roller.
Even if the felt web is adopted, the web amount assembled into the fixing device has an end portion (roll length) due to the maintenance cycle, the internal space of the apparatus, and the like.
If the web of the cleaning device runs out but image forming operation continues, the heat roller is quickly contaminated. In the worst case, the heat roller surface is scratched and cannot be used (must be replaced). Replacement of the heat roller requires a long time and high cost.
If the copying machine or printer apparatus is stopped when the web runs out, the serviceman mounts a new web, and the copying machine or printer apparatus can be used again without scratching the heat roller surface. However, the copying machine or printer apparatus cannot be used until the serviceman mounts a new web.